In the production of semiconductors, it is common to attach or secure a sputtering target to a backing member or plate in order to perform a subsequent sputtering operation. The backing plate to which the sputtering target is secured serves as simply a mount or fixture with which to hold the sputtering target during the sputtering operation. It is important to effect a secure bond between the sputtering target and the backing plate because of thermal and mechanical stresses generated during the sputtering operation which create a tendency for the target to delaminate or separate from the backing plate. This undesirable tendency is amplified or accentuated if there are voids or other structural defects or imperfections in the material which is used to bond the sputtering target to the backing plate.
Typically, a target is secured to the backing plate by soldering/bonding. However, the solder bond between the target and backing plate has often proved to be unacceptable from a structural integrity standpoint. Specifically, air pockets or air bubbles, commonly known as "voids", can occur in the solder bond between the target and the backing plate. Since voids decrease the amount of solder available to transmit forces between the target and the backing plate, stresses in the solder increase, sometimes exceeding the ultimate strength of the solder, resulting in target delamination or separation from the backing plate during the sputtering operation.
Another drawback of conventional soldering techniques, wherein a sputtering target is soldered to a backing plate, is the creation of a gap or recess in the solder bond at the peripheral edge of the interface between the target and the backing plate. This gap or recess occurs due to the fact that as the solder between the target and backing plate is cooled, it tends to shrink, causing the solder to recede or move toward the center of the target, leaving a gap or recess around the edge of the solder interface. This gap or recess further reduces the integrity of the bond between the target and backing plate.
A further drawback of conventional soldering methods is the entrapment of surface oxides in the solder layers that can lead to delamination and failure between backing plate and target.
It has therefore been an objective of the present invention to provide a method for soldering/bonding a target to a backing plate which eliminates, or at least reduces, the voids and surface oxides located or trapped in the solder bond.
It has been another objective of the present invention to provide a method of soldering a target to a backing plate which eliminates, or reduces, the gap which occurs at the peripheral edge of the solder interface between the sputtering target and backing plate.